This invention relates to the uses of silicon carbide (SiC) epitaxial layers grown on substrates offcut towards  less than 1{overscore (1)}00 greater than , to devices comprising such SiC epitaxial layers, and to a method of making such SiC epitaxial layers.
High doping concentrations are required to form low specific contact resistances in SiC ohmic contacts. Low ohmic contact resistances improve the performance of SiC devices. Conventional SiC homoepitaxy is performed on SiC substrates offcut towards the  less than 11{overscore (2)}0 greater than  crystalline direction. N-type doping concentrations are typically in the range of 1018 atomsxc2x7cmxe2x88x923, with some reports describing doping levels  greater than 1019 atomsxc2x7cmxe2x88x923, but higher doping concentrations and more efficient dopant incorporation (of both n-type and p-type dopants) are desired. Epilayers may offer lower defect densities and more controlled doping compared to substrate doping or dopant implantation into the substrate.
It is also desirable to provide a more uniform surface structure on the epitaxial layer surface. A uniform surface should facilitate the desired removal of material during device fabrication. A uniform epitaxial structure increases the ability to accurately predict how much material is removed during etching, and both the inter-wafer and the run-to-run etching variations are reduced. Smooth and uniform surfaces, especially in cases such as evaporated Schottky contact metals, will lead to improved device performance.
It is also desirable to have a more uniform surface to facilitate oxide formation and to reduce the density of interface trap states. Further, a more uniform epitaxial surface may reduce surface disparities that can lead to undesirable electric field emitter sites and ultimately premature oxide breakdown. Improved oxide properties will lead to improved device and passivation performance.
In SiC MOSFETs, the epitaxial layer comprising the channel can be polished to remove the steps on the surface that alter channel mobility (see S. Scharnholz, E. Stein von Kamienski, A. Golz, C. Leonhard, and H. Kurz, Material Science Forum, 264-268, 1001 (1998)). The polish will be more uniform with a more uniform step structure, and MOS performance will improve. The zig-zagged step structure found on SiC offcut towards the  less than 11{overscore (2)}0 greater than  is also likely to have a higher density of bonding disparities including dangling bonds that may cause high interface trap densities. Additionally, the large surface area exposed to ambient on the zig-zagged  less than 11{overscore (2)}0 greater than -offcut epitaxial surface may make this surface more reactive and prone to undesirable impurity incorporation.
It therefore is an object of the invention to provide an SiC material that minimizes or overcomes the problems of conventional SiC discussed hereinabove.
It is another object of the invention to provide a method of making SiC material of such improved character.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.
The present invention in one aspect relates to an epitaxial SiC film, grown on an offcut surface of a SiC substrate having a hexagonal crystal structure, with the offcut surface having an offcut angle of from about 6 to about 10 degrees, and the crystallographic direction of the offcut surface being towards one of the six equivalent  less than 1{overscore (1)}00 greater than  directions of the substrate xc2x17.5 degrees.
The invention in another aspect relates to a silicon carbide article, comprising:
a SiC substrate of hexagonal crystal form, with an offcut surface having an offcut angle of from about 6 to about 10 degrees, and the crystallographic direction of the offcut surface being towards one of the six equivalent  less than 1{overscore (1)}00 greater than  directions of the substrate xc2x17.5 degrees; and
an epitaxial SiC film, grown on the offcut surface.
The present invention relates in yet another aspect to silicon carbide epitaxial material, grown on a (0001) 4Hxe2x80x94SiC crystalline substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate.
The invention relates in another aspect to a 4Hxe2x80x94SiC epilayer film grown on a (0001) 4Hxe2x80x94SiC substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate, wherein the epilayer film has a LEED (0{overscore (1)}) beam intensity profile substantially as shown in FIG. 2, discussed more fully hereinafter.
A further aspect of the invention relates to a 4Hxe2x80x94SiC epilayer film grown on a (0001) 4Hxe2x80x94SiC substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate, wherein the epilayer film has an average root mean square roughness not exceeding about 2.0 nanometers, and preferably less than 1 nanometer.
Another aspect of the invention relates to a silicon carbide article comprising a 4Hxe2x80x94SiC epitaxial material on a (0001) 4Hxe2x80x94SiC single crystal substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate.
A still further aspect of the invention relates to a silicon carbide article comprising a 4Hxe2x80x94SiC epilayer film grown on a (0001) 4Hxe2x80x94SiC substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate, and having a LEED (0{overscore (1)}) beam intensity profile substantially as shown in FIG. 2 hereof.
In a still further aspect, the invention relates to a silicon carbide article comprising a 4Hxe2x80x94SiC epilayer film grown on a (0001) 4Hxe2x80x94SiC substrate offcut towards the  less than 1{overscore (1)}00 greater than crystalline direction of the substrate, and having an average root mean square roughness not exceeding about 2.0 nanometers, and preferably less than 1 nanometer.
As used herein, the term xe2x80x9csilicon carbide articlexe2x80x9d includes a silicon carbide epitaxial film on a silicon carbide base material. The silicon carbide base material may constitute a substrate body (e.g., wafer) formed of silicon carbide, or the silicon carbide base material may comprise a intermediate layer on which the silicon carbide epitaxial film is formed, for example as part of a multilayer microelectronic device (e.g., circuit) structure or as a part of some other structural body or form including the silicon carbide epitaxial film on the silicon carbide base material.
Concerning such device applications, the SiC films of the present invention may be employed for a wide variety of microelectronic devices or device precursor structures, including, without limitation, Schottky and p-n diode rectifiers, SiC photo-diodes and SiC light emitting diodes, switching devices, including field effect transistors (e.g., JFET, MOSFET and MESFET devices), monolithic integrated SiC operational amplifier chips, digital logic gates, latches, flip-flops, binary counters, half adder circuits, non-volatile random access memory (NVRAM) arrays and other SiC digital integrated circuits.
A broad method aspect of the invention relates to a method of forming a silicon carbide epitaxial film, comprising depositing such film on a silicon carbide crystalline substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate.
In another method aspect, the invention relates to a method of forming a silicon carbide epitaxial film, comprising depositing such film on a (0001) 4Hxe2x80x94SiC crystalline substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate.
A further method aspect of the invention relates to a method of forming a silicon carbide epitaxial film, comprising growing such film on a (0001) 4Hxe2x80x94SiC crystalline substrate offcut towards the  less than 1{overscore (1)}00 greater than  crystalline direction of the substrate, wherein the growing step comprises:
introducing a carrier gas, a vaporized silicon-containing material and a vaporized carbon-containing material into a growth chamber; and
maintaining the carrier gas, silicon-containing material and carbon-containing material flows and temperature condition for a time sufficient to grow a film of desired thickness.
The silicon-containing material and the carbon-containing material in the above method may comprise a single source material in which the source reagent contains silicon and carbon, in a single compound, adduct or coordination complex.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.